Systems and methods for improved spinal cord stimulation

ABSTRACT

Stimulation treatments for various medical disorders, such as neurological disorders, comprise novel systems, strategies, and methods for providing TMS, electrical, magnetic, optical and other stimulation modalities. Some stimulation methods comprise varying the stimulation parameters to improve the therapeutic efficacy of stimulation, and decrease risk of habituation and side-effects such as interference with normal brain, sensory, motor, and cognitive processes. The creation, and subsequent variation, of stimulation parameters can use sensed data in order to match, adjust, or avoid matching characteristics of the stimulation therapy relative to certain endogenous brain activities. Novel methods are described for choosing, creating and subsequently stimulating with partial signals which summate to produce therapeutic vector fields having unique temporal patterns and low- or high-frequency spectral content. Improvements for the treatment of pain are disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/241,524, filed Jan. 7, 2019, which is a continuation of U.S.application Ser. No. 14/334,371 filed Jul. 17, 2014, now U.S. Pat. No.10,188,864, which is a continuation of U.S. application Ser. No.11/307,050, filed Jan. 20, 2006, now U.S. Pat. No. 8,788,004, whichclaims priority of U.S. Provisional Application No. 60/593,521, filedJan. 21, 2005, entitled “Systems and methods for treatment of epilepsyand other neurological and psychiatric disorders”, and claims priorityof U.S. Provisional Application No. 60/594,321 filed on Mar. 29, 2005and U.S. Provisional Application No. 60/596,693 filed on Oct. 13, 2005,both entitled “Systems and Methods for Tissue Stimulation in MedicalTreatment”, and incorporates these prior applications herein in theirentirety.

FIELD

The present technology is generally related to a treatment program usedto guide stimulation treatments and includes providing novel stimulationsignals used by implanted stimulators or external stimulation devicessuch as magnetic stimulators, which can induce currents in the brain orbody of a patient, and which can be used in the treatment of medicaldisorders such as neurological, movement, and psychiatric disorders, orother disorders of the brain or body, and is particularly relevant toreducing the incidence of epileptic seizures.

BACKGROUND

There are several problems which are encountered when providingstimulation, such as neurostimulation, in the treatment of a disorder.One problem is that the stimulation field is not optimally focusedwithin a target area, and stimulation occurs in adjacent areas. Forexample, providing low frequency stimulation to one area may assist intreatment of some types of disorders such as epilepsy, while this samestimulation causes side-effects by unintentionally stimulating adjacentareas. If the target tissue is distal from the electrode, theintervening tissue will usually be stimulated with the stimulationpattern which is intended for the target area. Providing certain typesof stimulation to treatment areas, while supplying different types ofstimulation to non-target areas, can decrease the occurrence ofside-effects and enable improved treatment. Other problems which arisewhen electrically stimulating tissue are related to the transfer ofenergy from the electrical contact to the immediately adjacent tissue aswell as through tissue itself. While certain types of stimulus waveformsmay be good for treatment, these may be less well suited fortransmitting energy from the electrodes to tissue, and subsequentlythrough tissue itself. One approach to optimizing the desired effects ofstimulation is to construct a “carrier wave” comprised of an oscillatingcarrier such as a train of high frequency pulses at some high frequency,f(H), which is modulated by some lower frequency mf(L) or contour mc(L).The contour itself may be an arbitrary waveform, a sine wave, anenvelope derived from sensed activity, or a ramp of a specified rate ofchange of amplitude. This approach may be improved by changing thecarrier frequency f(H) or by changing the modulating contour or itsfrequency at specified or random intervals, in order to increaseentrainment and avoid habituation or adaptation to the stimulation.Another solution is to use signals which have desired characteristicsfor stimulation of, or transmission through, tissue which is not thetarget tissue, and which combine to create a vector field whichstimulates target tissue in a desired manner. While methods of combiningstimulation signals to produce desired vector fields have been used fordermal stimulation, and stimulation of other tissue, the methodsdescribed here are novel from, and offer advantages over, those of theprior art.

PRIOR ART

The methods and systems of the current invention are novel from andadvantageous over prior art that has addressed the some of the issuesdescribed above. For example, US 20030135248 entitled ‘Variation ofneural-stimulation parameters’ (the '248 application) describesimproving therapy, and minimizing energy consumption, side-effects, andtolerance by pseudo-randomly varying at least one parameter andsimultaneously varying a second parameter based upon a predeterminedrelationship specifying how the changes in one parameter affect thevalues for the second parameter with respect to neural excitation (e.g.,with respect to the strength-duration relationship). The idea here isthat it may not be possible to achieve the desired therapeutic effectwithout unwanted side-effects of stimulation when a large volume oftissue is simultaneously modulated. By pseudo-randomly varying thespatial pattern of the modulated neural structures, it may be possibleto minimize undesired side-effects such as adaptation to the stimulationsignal while still attaining the desired therapeutic efficacy. Althoughthis prior art varies stimulation at one electrode based uponstimulation at another, it does not discuss a method of diminishingside-effects by providing subthreshold stimulation (e.g., due tospectral content) at multiple leads which are physically configured sothat the energy combines to the extent needed for clinical efficacy(e.g., as an interference pattern, a harmonic or a sub-harmonic, orotherwise produces effective stimulation frequencies) primarily in thearea where neurostimulation is desired, which is part of the claimedinvention.

The methods and systems of the current invention are also novel from andadvantageous over prior art that has addressed the issues of fixedelectrode placement. For example, US 20020022866 entitled ‘MultichannelStimulator Electronics and Methods’ and U.S. Pat. No. 6,662,053 (both toBorkan) describe improving therapy by providing a system for virtually“repositioning” electrodes by changing the strength and otherstimulation parameters in order to reshape the electrode field. Thisnon-invasive repositioning may be advantages in cases of post-surgicalelectrode-migration, when surgical placement fails to produce results,and to “accommodate” endogenous alterations which may cause the exacttarget location to change over time. Similarly in U.S. Pat. No.6,393,325 (to Mann et al) “Directional programming for implantableelectrode arrays” is described in which the position of the stimulationfield is virtually readjusted after surgery by programming the array todeliver stimulation at different locations in the tissue. In US20030078633 (to Firlik et al.), systems and methods for providingtranscutaneous and subcutaneous stimulation are provided which rely uponmultiple electrode locations in order to provide stimulation fields ofdifferent shapes and strengths, mostly oriented towards spinalstimulation, although these can be used for other types of stimulationas well. The Borkan, Firlik, and Mann inventions are designed tonon-invasively alter the size, shape, orientation, and position of thevector field. These do not describe using temporal and spectral signalswhich produce different stimulation effects in the vector field thanthose which are produced in non-target areas, which is a primaryadvantage offered herein. Further, the prior art doesn't describe oranticipate using spectral and temporal characteristics of the vectorfield to decrease side-effects, and tolerance by pseudo-randomly varyingat least one parameter, which is part of the present invention. Themethods and systems of the current invention are novel from andadvantageous over other prior art as well, as is partially illustratedin the following objects of the invention. There is disclosed an objectof providing a unique stimulation signal to a neural target relative toadjacent areas. In one embodiment two or more stimulation leads areused, which are located proximal enough to permit the summation of avector field having spectral content that stimulates a desired area toprovide therapeutic benefit, while not imposing this type of stimulationin adjacent areas. Accordingly, the fields outside the target areastimulate the non-target areas in a differential manner or do notstimulate these areas. There is also disclosed using two or morestimulation leads which stimulate at subthreshold levels (e.g., usingineffective waves-shapes), in order to reduce the amount of side-effects(which occur in non-target tissue), but which are positioned andoriented to cause their fields to combine effectively to produce therapyin target tissue.

These and other features of the claimed invention will expanded upon inthe following material which describes numerous preferred embodiments ofthe systems and methods. It is obvious that the exact details foraccomplishing the embodiments described herein can be modified withoutdeparting from the spirit of the inventions.

SUMMARY

Illustrative embodiments of the invention are provided, which overcomethe above noted, and other, deficiencies of alternative methods andsystems of stimulation, such as those currently relied upon bymultiple-lead stimulators. The illustrative embodiments providetechniques for improving stimulation, which may be deep brainstimulation, to treat various disorders, by decreasing the risk of usingincorrect stimulation parameters, stimulating non-target tissue;development of tolerance; and other unwanted effects. Whileneurostimulation, especially with respect to treatment of seizures, isemphasized in some of the material here, the treatment of otherdisorders of the brain and body are also described and are no lesscentral to many of the advantages of the inventive principles.Accordingly, the stimulation techniques described here can be applied tothe brain, the spinal cord, cranial and vagus nerves, or other area ofthe body, during modulation for the treatment of disorders, such asepilepsy, psychiatric conditions, migraines, headaches, pain, tremor,and depression, traumatic brain injury, cerebovascular accidents,strokes, thrombosis or aneurysm, or used for the treatment of disorderssuch as cardiac disorders which can be treated via CNS targets or bydirect stimulation of cardiac tissue. Stimulation can also be appliedfor treatment of wounds, infection, degenerative disorders, injury,healing acceleration, bone growth, and promotion and direction ofcertain types of cell growth and metabolic activity. The systems andmethods of the invention can also be applied to the vagus and othernerves related to modulation of the central and peripheral systems (e.g.unilateral or bilateral stimulation of the trigeminal nerves), and canalso be applied to stimulation of other areas of the body such as thecardiovascular system, digestive system, skin, muscle, spine, nervesrelated to pain, or other tissues or organs. Further, sensed datarelated to any of these disorders can be sensed from both the brainand/or body. Sensing and stimulation can occur in regions of the brainand body which are the same or different.

In one embodiment, a treatment parameter is systematically varied, andsensed data are collected and processed, in order to determine whatvalues successful led to desired treatment effects. These successfulparameters can then be selected and relied upon for during treatment.

In another embodiment two or more electrode leads each stimulate usingpartial stimulation signals of different spectral compositions. Forexample, the stimulation signal to be used at each electrical contactcan be added to an interference signal, so that the vector summed signalin the tissue approximates the stimulation signal (e.g., FIGS. 5a, 5b ).Alternatively, each lead can use a stimulation signal having stimulationfrequencies which are separated by a frequency which is a beatfrequency, which, for example, may be maintained within a specifictherapeutic frequency range over time (e.g., between 4 and 8 Hz).Further, the instantaneous frequencies of two signals can be variedconsiderably while maintaining a constant beat frequency, for example,in order to decrease tolerance or increase entrainment to thestimulation or to avoid certain side effects in the non-target tissue.In a preferred embodiment of the present invention to utilize beatstimuli which are created from stimulation at two or more electrodecontacts, the stimuli being modulated at least at two different rateswhich differ between at least approximately 0.5 Hz and at most byapproximately 20 Hz.

The invention uses vector field signals which are determined to beclinically effective. The sets of partial frequencies which create thetherapeutic vector signals when provided at specific electrodes (withconsideration to electrode geometry when appropriate) can be chosen andtested automatically, or by a physician or patient. Sets of partialfrequencies which provide therapeutic stimulation while not producingunwanted side-effects can be stored in a database and selected fortreatment. These sets can then be chosen and utilized according tosensed data, according to time information, according to patientrequest, or by other methods.

The use of partial stimulation signals can be beneficial because onlythe target tissue (e.g., neuroanatomical area) which is commonlyinfluenced by the stimulation signal of two or more electrode leads willbe stimulated with the vector signal while other areas, within whichstimulation may not be necessary, are not stimulated by the vectorsignal. Accordingly, the target site can be stimulated with a lowfrequency while adjacent non-target sites are stimulated using asignificantly different frequency range. In other words, thetarget-signal and non-target signal generally have different spectral,spatial, and temporal characteristics, which can cause, or not cause,modulation of tissue or which can selectively modulate certain celltypes. In one embodiment of this method, two or more stimulatingelectrodes are positioned so that their combined fields can superimposeat, or near, the areas of epileptic foci. By increasing the strength ofthe stimulation at a subset of the electrodes, with consideration ofelectrode geometry, the spectral content and area of maximumsuperposition can be adjusted. The adjustment of the spectral andtemporal content of the stimulation signals and the vector field, andthe shape of these fields can be assisted by an external patientprogrammer, which has graphical displays of the field properties thatenable a user to custom tailor the treatment for a patient, and whichcommunicates with one or more stimulation devices providing the therapy.

Some stimulation methods comprise varying the stimulation parameters toimprove the therapeutic efficacy of stimulation, and decrease risk ofhabituation and side-effects such as interference with normal brain,sensory, motor, and cognitive processes.

Other advantages, novel features, and further scope of applicability ofthe invention will be described in the following illustrations anddescription.

BRIEF DESCRIPTION OF DRAWINGS

For the purpose of illustrating the invention and its advantages, thereis provided a detailed description and accompanying drawings ofembodiments which are presently preferred. In illustrations of themethods, when arrows indicate iteration (a return from later steps toprior steps), this iteration is understood to be a preferred embodiment,and executing the steps a single time may also be an option. In theillustration of methods, steps which occur sequentially may also occurconcurrently, in parallel, or may be repeated several times (e.g., inorder to obtain an estimation of a measure by computing a statistic suchas the mean), prior to the next step occurring. It is understood thatthe invention is not intended to be limited to the precise arrangementsand instruments shown, wherein:

FIG. 1a shows a schematic representation of one embodiment of aneurostimulation system which can be used in the current invention,

FIG. 1b shows a schematic representation of an alternative embodiment ofa neurostimulation system which can be used in the current invention,which provides drug stimulation, in addition to other types ofstimulation:

FIG. 2a shows a schematic block diagram representation of a systemdesigned to create partial signals to be used during neurostimulation,this can be implemented m the stimulation sub system:

FIG. 2b shows a schematic block diagram representation of method ofusing a system designed to create partial signals to be used duringneurostimulation:

FIG. 3a illustrates an embodiment of an implantable stimulation systemincluding a device having 6 electrodes that are implanted in the neuraltissue of a patent;

FIG. 3b illustrates an embodiment of an implantable stimulation systemincluding a device having 2 stimulation arrays located bilaterally to apatient's spine;

FIG. 3c illustrates an embodiment of a display screen which is part ofan external patient programmer which displays the shape, location,orientation, strength, spectral, and other characteristics of two ormore stimulation fields of the partial signals and the vector field:

FIG. 4a shows example embodiments of partial signals, where signal #1and signal #2 are partial signals which can be combined to form a vectorsignal which is a combined signal, and where the partial signals have asubstantially different frequency content than the combined signal;

FIG. 4b shows alternative example embodiments of partial signals andvector signals, including pulsatile and modulated-pulse signals:

FIG. 5a shows a schematic representation of the operational flow of amethod designed in accordance with a preferred embodiment of the presentinvention, wherein two partial signals are created by addinginterference signals to a low frequency base signal;

FIG. 5b shows a schematic representation of an alternative methoddesigned in accordance with a preferred embodiment of the presentinvention, wherein two partial signals are created by addinginterference signals to a high frequency base signal,

FIG. 6 shows a schematic representation of an alternative methoddesigned in accordance with a preferred embodiment of the presentinvention, wherein two partial signals are created by splitting, orotherwise deconstructing, a base stimulation signal, and wherein thesepartial signals are subsequently re-assigned to different contacts atdifferent moments in time;

FIG. 7 shows a schematic representation of another method designed inaccordance with a preferred embodiment of the present invention, whereina parameter of the stimulation signal, such as the frequency of a signalis roved, or alternated, between at least two frequencies, during thetherapy;

FIG. 8 shows a schematic representation of an alternative methoddesigned in accordance with a preferred embodiment of the presentinvention, in which rather than relying upon the creation of newstimulation signals, stimulation signals are modified before beingapplied in order to alter the stimulation signals at different momentsin time;

FIG. 9 shows a schematic representation of another method designed inaccordance with the present invention, wherein the stimulation signal istemporally distributed across a number of stimulation locations; and,

FIG. 10 shows a device for providing responsive and/or non-responsivetranscranial magnetic stimulation to a patient.

DETAILED DESCRIPTION

This specification describes improved systems and methods forstimulation of tissue, which may include deep brain neurostimulation.The following material provides a general understanding of terms used inthis specification, with the understanding that these terms can befurther adjusted or modified or altered within the specification itselfto achieve different specific embodiments of the invention.

As used herein the terms “stimulation system” or “stimulator” refers toa device comprised of components which are either configured in adistributed manner or are primarily contained within the housing ofdevice such as an implantable device, and which can modulate tissue bydelivering one or more of electrical, optical, magnetic, or drugtherapy. The stimulator can be a generic implantable stimulator such asthose manufactured by Medtronic, NeuroPace, Cyberonics, NeuroBionics,and Advanced Neuromodulation Systems, which can be configured or adaptedto provide electrical stimulation according to protocol that may befixed or which may be adjusted based upon a clock signal and/or state ofa patient. In some embodiments, the stimulator can also include ageneric drug pump, such as those manufactured by Medtronic, Johnson &Johnson, or Advanced Neuromodulation Systems, which can be configured oradapted to provide drug stimulation according to a fixed protocol, or inresponse to a clock signal or sensed data. Accordingly, the stimulator10, can be realized, for example, using either electrical signalgenerating stimulators 10 a, or a combination of the two 10 b. Thestimulator can also take the form of a transcranial magnetic stimulator,sonic, or other stimulation device, with components located partially orcompletely outside of the patient.

As used herein the term “stimulation conduit” can include one or moreelectrical leads, each having at least one electrical contact. Thestimulation conduit can also be one or more electrical contacts of alead. The stimulation conduit can also be one or more catheters, each ofwhich can be a simple catheter or a combination catheter/lead alsocapable of providing electrical stimulation or sensing in conjunctionwith drug delivery. The stimulation conduit can also include an opticalfiber or transducer, including infrared generating devices, or may berealized as an electromagnetic coil, and can include sound transducersincluding those related to the providing ultrasound treatment.Stimulation conduits can be configured to be configured to be positionedin, on, near, or otherwise adjacent to tissue, such as nerve tissue andneurons, and can include a number of embodiments including plateelectrodes, percutaneous leads (e.g. a tripole percutaneous lead),circumferential leads, laminotomy, paddle, and bifurcated stimulationleads, cuff leads, and directional electrodes.

As used herein, the term “sensor” can refer to a device for measuring anelectrical, chemical, optical, or other physical property of thepatient. A sensor may provide sensed data relating to multiple measures,for example, the flow rate, concentration, and pressure of a fluid.Accordingly, a sensor may be an aggregate of several types ofspecialized structures each configured to sense a differentcharacteristic of the environment in which it is located. The sensorscan also include electrochemical sensors (e.g., microelectrode arraysmade by Quanteon for measuring substances such as glutamate), or opticalsensors (e.g., which can detect O2, CO2, and PH levels, and which cantake the form of pulse oximeters or chromophore-based IO biosensorshaving one or more sensing fibers), and can detect physical measures(e.g., pressure, temperature, flow, acceleration), enzymatic changes, orthe state of tissue or an organ. The sensor can be an electrical contactthat may also provide stimulation at times which sensing does not occurat the contact. The sensors can be biosensors which are capable ofsensing one or more specific molecules or other biological substances,either directly or by means of their metabolites. The sensors can alsobe biosensors, or equivalents such as a chemically sensitive/enzymesensitive field effect transistor, capable of sensing neurochemicalssuch as neurotransmitters. U.S. Pat. No. 5,791,344 to Schulman et al.entitled “Patient Monitoring System,” proposes a system to monitor theconcentration of a substance in a subject's blood wherein one enzymaticsensor is inserted into a patient to monitor glucose. Similarly,EP1011797 to Schulman et al, entitled “System of Implantable Devices forMonitoring or Affecting Body Parameters,” proposes using microsensors tomeasure, for example, glucose level, oxygen content, temperature, andother measures. A sensor may sense, for example, EEG, neurotransmitterlevels, cardiovascular measures such as heart or respiration rate,glucose level, oxygen saturation level and other types of information inorder to measure state of the subject.

When possible, the invention can rely upon completely implanted sensors,but may also communicate with, external devices, or may utilizeinformation derived from assays, or laboratory techniques, in order toobtain accurate sensed data of the desired measures. In the casedisorders such as a movement disorder, a sensor may be a motiondetector, microphone, or EMG sensor implanted, for example, in a limb(the data of which can be filtered and processed in order to alsomeasure the patient's EKG and its related measures such asinterbeat-interval), or can be an EEG sensor located, for example, oversomatosensory/motor areas of the brain. The sensor can communicate withand obtain power from the stimulator 10 or can have its own power sourceand communicate via telemetry, or by optical or sonic signal, and canalso be a device external to the patient which communicates with thepatient programmer or stimulator 10. Alternatively, one or more sensorscan communicate with the stimulator for example, the control subsystem20 using a port/bus, with address, data, control lines and otherhardware required for successful communication. Analog-to-digitalconversation, and conversion of raw data to meaningful units (e.g.,signal processing, such as measuring the power in a limited frequencyband after time-to-frequency conversion of the data, can reflect thesize of a tremor) can occur at the level of the sensor or can occur inthe stimulator 10.

As used herein “treatment program” determines the parameters for thestimulation, sensing, and evaluation protocols, or determines, if, how,why, and when the protocols are altered. The treatment program can beimplemented in hardware (e.g., a control circuit) or software form andcan be implemented by the control subsystem 20 for providing treatment.The term “treatment” can simply mean decreasing or deterring one or moreunwanted symptoms of a disorder or creating an advantage which would notoccur if treatment wasn't provided. The treatment program can utilizetreatment parameters and protocols in order to modify any method of thetreatment, including modification and control of operations andprotocols which perform sensing, evaluating sensed data, or stimulating.

As used herein “stimulation subsystem” provides stimulation, via atleast one stimulation conduit, according to the parameters of astimulation protocol which determine where, when, and how to stimulatewith, for example, one or more of electrical, optical, or otherstimulation. Not only the type of stimulation but also the number andlocation of sites at which stimulation can occur are defined by thestimulation protocols. The stimulation protocol can be selected oradjusted based upon time information, sensed data, the state of thepatient, or a combination. A stimulation parameter can determine each ofthe characteristics of a stimulation protocol, such as level ofstimulation (e.g., voltage or current), occurrence of stimulation (e.g.,duration, duration per unit of time), type and site of drug delivery,signal characteristics such as signal shape and many othercharacteristics as is known in the art. A stimulus parameter can be aspectral parameter, which relates to the amplitude, phase, and frequencyof at least one component of the stimulation signal. A stimulusparameter can also be a pulse parameter, such as pulse frequency,amplitude, width or shape. The overall shape of the stimulation signalcan also be sinusoidal, arbitrary, or can approximate differenttrigonometric functions.

As used herein the term “sensing subsystem” refers to a subsystem whichprovides sensing according to the parameters of a sensing protocol whichdetermines where, when, and how to sense with one or more sensors whichmay detect, for example, electrical, optical, or chemical information.The sensing subsystem may have a detection subsystem module which isconfigured to detect and or measure specified events, or states, and caninclude programmable signal conditional circuitry and algorithms. Thesensing protocol can be selected, or adjusted, based upon, for instance,time information or the state of the patient or both.

As used herein the term “control subsystem” refers to a subsystem whichprovides control of the treatment and can implement a treatment program.If sensed data are obtained by the stimulator, the control subsystem canrely upon an evaluation protocol to determine if, when and how toevaluate the sensed data and determines if stimulation occurs inresponse to the sensed data. The evaluation protocol can be selected oradjusted based upon time information or the state of the patient, orboth. The control subsystem can also use a control circuit to implementcontrol laws based upon measures of sensed data, provided by the sensingsubsystem, in order to enact therapy.

As used herein the term “treatment criterion” usually refers to acriterion to which sensed data are evaluated or compared using theevaluation protocol. The results of this comparison can determine whattype of stimulation takes place. For example, failure to meet atreatment criterion may cause stimulation to occur or may cause a changein a protocol parameter, or may cause a different stimulation protocolto be selected. Alternatively, success in meeting a treatment criterionmay cause stimulation to be halted or may cause the same stimulationprotocol to be selected again. It is obvious that the logic of treatmentcriterion can be inverted, and several criteria can be combinedsequentially or in parallel in order to provide therapy withoutdeparting from the spirit of the invention illustrated and described inthe embodiments of this description of the invention.

As used herein, “basal signal” or “basal stimulation” refers to theapplication of stimulation intended either to decrease the probabilityof an adverse event occurring, such as a seizure, or to modulateactivity related to a disorder such as psychiatric illness or tremor.The basal signal is generally applied non-responsively, continuously, orperiodically applied, although it can be adjusted or selected based uponthe treatment program, time information, or sensed data.

As used herein, “base signal” normally refers to a signal which will bemodified or used to determine two or more partial signals. The partialsignals will normally combine to form a “vector sum field”, in thetissue of the subject which approximates the base signal.

As used herein, “responsive” stimulation refers to the application ofstimulation which occurs in response to evaluation of sensed data, suchas the detection of a medical event, state, or activity related to asymptom of the disorder.

As used herein, the terms “event”, “detection of event” or “medicalevent” refer to the sensing of data and the analysis of this data whichconfirms that abnormal or unwanted activity, such as a seizure, tremor,or other activity related to a disorder was detected, or indicates thator at least one biochemical index has assumed a value that is above orbelow a specified criterion.

As used herein, “seizure” refers to behavioral or electrophysiologicalsignature of an impending or existent seizure, and includes epileptiformactivity.

As used herein, “amplitude” may refer to either voltage or current of astimulation signal (while the other is held constant or also varied),and may be scaled or adjusted based upon impedance characteristicsand/or electrode geometry.

FIG. 1a is a schematic of the components of a preferred embodiment ofthe stimulator 10 a and includes a control subsystem 20 a stimulationsubsystem 22, a power source 26, such as a rechargeable battery, and amemory storage structure such as a database 28. The control subsystem 20contains electronics which are commonly incorporated into implanteddevices such as specialized circuits for carrying out the tasks involvedin providing stimulation therapy (e.g., see U.S. Pat. No. 6,066,163,US20020072770, and US20050240242). Accordingly, the control subsystem 20can contain telemetry circuits, programmable memory, a microprocessor, atimer/clock, multiplexors, switches/relays and other components whichare used currently within implantable stimulators as is known to thoseskilled in the art. Similarly, the stimulation subsystem 22 can includehardware needed to provide transduction of different pulses and otherwaveshapes, and transduction means for providing electrical, optical,magnetic or other type of stimulation. The stimulation subsystem 22 caninclude programmable signal generators, amplifiers, filters, DSPmodules, regulating circuitry for voltage, current, impedance (e.g.,impedance sensing and matching circuitry for both high and low impedancestates associated with different signals and endogenous conditions andvariable impedance networks), polarity and charge-balancing operations.The stimulation subsystem 22 can program the conduits to stimulate in abipolar, monopolar, or in both modes, containing one or more polarityswitches. The stimulation subsystem can provide independent amplitudeand stimulation control for each of all the stimulation conduits and caninclude inter-electrode sensing and calibration circuitry and routinesfor adjusting the partial signals to produce the intended vector fieldin the intended location as well as circuitry for changing the size,shape, position, spectral and temporal characteristics of the vectorfield.

In order to create stimulation signals a programmable frequencygenerator can be used by the stimulation subsystem 22 which sends asignal to a pulse-width control module for creating pulses which aresent to a digital-to-analog converter and an amplifier for amplifyingthe signal that is to be used during treatment. Additionally, pulsewidth/amplitude circuits can be used. The stimulation subsystem 22 canalso include hardware and/or software for providing the treatmentsdescribed in this application, including, for example, partial signalssuch as can be generated using methods and systems shown in FIG. 2a andFIG. 5b . A clock can be included in the control subsystem 20 to providetime information in order to permit the control subsystem 20 to selector adjust stimulation protocols based upon time information. Theprotocols can be stored in the memory, which is realized here as aquerieable database 28, which permits the control subsystem 20 to obtaininformation such as stimulation parameters for various stimulationprotocols, self-norm data, and other information relevant to providingtherapy. At various times prior to, during, or after implantation, thecontrol subsystem 20 can be programmed to select or adjust protocols inrelation to predetermined counts of the clock, durations (e.g., timesince the last stimulation protocol was selected), or times of day. Thepatient may adjust the therapy program of the control subsystem 20 toprovide stimulation via the stimulation subsystem 22 using stimulationprotocols that are selected or adjusted. The control subsystem may alsobe supplied with memory for computational needs. The stimulationsubsystem 22 can be controlled by an external patient programmer whichallows the patient to select different stimulation protocols, differentstimulation waveforms and different sets of partial signals and theirassociated montages and characteristics. Using a graphical userinterface of the external programmer, a medical professional can directthe stimulation subsystem 22 with respect to the characteristics of thestimulation protocol to use at any particular electrode and also toshape or move the virtual vector field in a particular fashion. Thecalibration method displayed in FIG. 2b can be used in order tocalibrate or confirm the model used by the subsystem 22 or externalpatient programmer.

Although shown as separate components for purposes of illustration, thecomponents of FIG. 1a and many of the other FIGS. provided herein cangenerally be realized on a single circuit board, and can even berealized as a microchip which contains specialized circuitry foramplification, DA/AD conversion, digital and analog signal processing,memory, timing, clock, and communication circuitry which are powered bya power source. When the stimulator provides drug therapy, theelectronics of the stimulation subsystem 22 can supply control of, andpower to, one or more pumps for dispensing one or more drugs, stored ina reservoir assembly, according to the stimulation protocol.

FIG. 1b is a schematic of another preferred embodiment of the stimulator10 b and includes a control subsystem 20, a stimulation subsystem 22, asensing subsystem 24, a power source 26, and a database 28. The sensingsubsystem 24 can provide analog-to-digital conversion circuitry, memory,multiplexing circuits, relays, signal processing circuitry, or othercircuitry which is not provided in the control subsystem and which isneeded to obtain, analyze, amplify, process, and store the sensed dataobtained from at least one sensor. The sensing subsystem 24 can performprocessing of the sensed data, such as amplification, signal processing,filtering, spectral analysis, time-frequency analysis, state-analysis,modeling, comparison operations which can be statistically based andutilize logic operations, and can provide for temporal analysis andpattern matching as may be used to detect epileptiform, tremor, or otheractivity related to the disorder being treated. The sensing subsystem 24senses data according to the parameters of a sensing protocol. Astimulator conduit, such as 30 of FIG. 3, can be realized as leads, eachof which serve both as a stimulating electrode and also as a sensor.Each contact 32 a-32 f can serve both as a sensor, when the contact 32functionally communicates with the sensing subsystem 24, and as astimulator, when the contact 32 communicates with the stimulatingsubsystem 22. The physical connection between the contact 32 and eitherthe sensing 24 or stimulating 22 subsystems can be controlled by amicro-relay or switch, such as a make-before-break double-throw relaywhich can be located in the control subsystem 20. Alternatively, sensors34 and contacts 32 may be physically distinct, for example, as in thecase where the sensors 34 measure optical, chemical, pressure,temperature, movement, or other physical aspect of the region from whichthe sensed data are obtained. The electrical stimulation/sensing can bemediated directly by the control subsystem 20, or can be accomplished bymeans of the stimulation and sensing subsystems 22, 24, which are undercontrol of the control subsystem 20, as is the case for drug deliveryFIG. 1b . When stimulation includes the delivery of drugs, then thesecan be dispensed through the drug conduits of the stimulation subsystem22.

When used to treat seizures, at least one sensor 34 can be situated in abrain region, such as an epileptogenic lesion, an epileptogenic region,a spike focus, a focal functional deficit, an irritative zone, astructure of the limbic system, or the temporal lobe, or any structurewhich is characterized by abnormal electrical or neurochemical activity.Alternatively, when used to treat pain one sensor 34 can be in thebrain, spine, or peripheral nerves to detect activity related to pain,and the stimulation electrodes can be located to stimulate target areasof the vagus nerve. Further when used to promote chemotherapy a drugsensor 34 can be in a region near a tumor, and the stimulationelectrodes (or external magnetic stimulator coils) can be located tomodulate electroporation, or activation of a nano-particle containingdrug, which is approximately localized to the tumor target by thespectral, temporal, or other characteristics of the vector field.Generally, by using multiple electrodes to stimulate a given area thesemay each stimulate in a subthreshold manner, while the energy in theanatomical area that is commonly stimulated by the different electrodes,can summate and produce a signal with characteristics (e.g., spectralcharacteristics, pulse shapes, and current/voltage strength) which canmodulate the target tissue to provide the intended therapy either alone,or in conjunction with other therapies.

FIG. 2A shows a schematic representation of a system designed to createpartial signals which are used during stimulation. This system can beincorporated into the stimulation subsystem 22. A signal creator 40works with a partial signal creator 42 in order to create the partialsignals. In one method the signal creator 40 supplies a base signal to apartial signal creator 42, which then modifies the signal to create anumber of partial signals. For example, by adding selected interferencesignals to the base signal, partial signals can be created so that theirsummation leads to a vector field which is approximately the basesignal. The size and polarity of the interference and partial signalscan be adjusted, by the partial signal creator, based upon an algorithmwhich incorporates the spatial location and orientation of the electrodecontacts (or optical outputs). In an alternative method, the signalcreator 40 controls the partial signal creator 42 and directs it toprovide the partial signals according to a specified algorithm. In oneinstance, where the intended vector signal is a beat at a particularfrequency, the algorithm can choose 2 partial signals that are separatedby a specified frequency. The partial signals can also be generateddigitally using algorithms, using analog circuitry, or can be selectedfrom a database 28 of predefined partial signals. In one type ofsubtraction algorithm, filtered versions of the base signal areiteratively obtained (and may be subtracted from a base signal to ensureorthogonal spectral content) in order to create partial signals. Thepartial signal creator 42 can also generate the partial stimulationsignals based upon calculations made upon data contained in the database28, such as sensed calibration data or user inputted data. Partialsignal generation may also include information about the number of leadsactivated during stimulation, the 2-dimensional positions of leads, the2-dimensional inter-lead distances, the 3-dimensional positions ofleads, the 3-dimensional inter-lead distances, the bipolar or unipolaractivation mode for each lead, the 3-dimensional positions of grounds,and approximate impedances of the leads. The creator 42 can generate atleast two partial stimulation signals based upon these calculations inorder to produce approximately the desired electrical field summationsignal in approximately one or more target tissue regions.

In any case, regardless of the methods used, once the partial signalsare created these are then directed to their intended contacts 32 by thesignal router component 44, which also may be realized within thestimulation subsystem 22 and which can contain digital-to-analogconverters, filters, amplifiers, switches, charge balancing and biasingcircuits, and mutliplexors, each of which can be separate components orwhich can be embodied into a specialized microchip. The components ofFIG. 2a , can operate to provide continuous stimulation, or can beoperated responsively, when sensing is combined with the illustratedsteps of the method, and can activated iteratively, as might occur toprovide different partial signals as therapy continues.

FIG. 2b shows a schematic representation of a method of using a system,such as that of FIG. 2a , that is designed to create partial signalsthat are to be used during stimulation. The first step is to create orselect at least one stimulation signal 50 to be used during treatment.The stimulation base signal is then transformed into two or more partialsignals 52 which are provided at each of two or more contacts 54. Duringstimulation treatment, the actual summation of the partial signalswithin the target tissue will deviate from intended summation dependingupon factors such as conductance, impedance, and the actual physicallocation and orientation of the electrodes. In one embodiment of acalibration method which is used, from time to time, the partial signalsare adjusted based upon data which is sensed concurrent withstimulation. For example, a calibration signal which may be at least onepartial signal is used to stimulate contact set “i” of N contacts 54,and data are sensed at contact set “j” 56, where sets “i” and “j” eachinclude at least one contact. The sensed data allows empiricalmeasurement of the electrical field and can be used to adjust thepartial signals 58 so that the actual field vector more closelyapproximates the intended vector field in 3-dimensional space. Thisprocess can be iteratively repeated several times until the sensedsignal is calculated to be within some tolerance level with respect tothe intended signal. When stimulating with optical signals, theorientation and beam paths can be taken into consideration by thepartial signal creator. In that instance, calibration used to adjust thepartial signals 58 can be obtained using optical sensors that senseoptical strengths of various light sources 56. When used with opticalstimulation, in addition to the pattern of activation, different opticalstimulation conduits may emit different frequencies of light atdifferent locations, or different frequencies may be emitted from thesame conduit at different moments of time.

FIG. 3 a Shows a generic implantable stimulation device 10 that has astimulation conduit which includes six electrical contacts (32A-F) thatare implanted in the neural tissue 36 of a patient 38. The implantablestimulator 10 contains signal generating and computational circuitry, apower supply, sensors and other components which are commonly foundgenerically in implantable stimulators such as has been described inU.S. Pat. No. 6,066,163, US2002/0072770, & US2004/017089. The stimulatormay also be realized using the neurostimulators 10 a, 10 b shown in FIG.1a and FIG. 1b . The stimulator device 10 can contain a general accessport 6 which serves different functions in different embodiments, forexample, the access port 6 can comprise a re-sealable septum whichaccepts a needle for replenishing fluids used in drug delivery, or theaccess port 6 can accept a control link from an external controllerdevice. The device 10 can also contain a connection port 8 forconnecting, for instance, to sensors 34 which can provide sensed data,or which can accept a signal from another implanted device forpermitting two or more devices to collaboratively provide treatment.Although shown in a single region, the stimulation electrodes can belocated in subsets provided in different regions of tissue, and may berealized in a unilateral, bilateral, or other treatment montage.

The present invention can assist in stimulating target tissue moreprecisely and can decrease side-effects of stimulation. In one generalembodiment, stimulation occurs at two or more stimulation leads tocreate selected stimulation signals in approximately a target area,while stimulating with other signals in approximately non-target areas.The intended stimulation is thereby increasingly localized, since targetareas are differentially stimulated with respect to non-target areas. Inone more specific preferred embodiment, in a stimulation treatment, twoor more electrical contacts each with stimulation signals comprised offrequencies which are separated by a specific range (e.g. differing byapproximately 0.1 Hz to 20 Hz) can be used wherein each of thestimulation signals is output from a different contact, and wherein thecontacts are sufficiently close that the fields can partially intersect.In one illustrative example, a 40 Hz stimulation signal is emitted fromstimulation lead 32A, of FIG. 3a , and a 43 Hz stimulation signal isgenerated at stimulation lead 32C, which causes a beat frequency of 3 Hzto be induced in the tissue which is commonly stimulated by bothstimulation leads. The spectral content of the partial signals can varywidely without changing the beat frequency. The vectors signal cancontain energy from approximately 0.5 to 20 Hz, while the partialsignals contain energy which is at least 25 Hz, and in that range, orthe partial signals can contain energy between 80 and 200 Hz. In onepreferred embodiment, the vector signal (or its rectified equivalent)contains a majority of its energy approximately below F1 Hz, while thepartial signals (or their rectified equivalents) contain energyapproximately above F2 Hz. In this embodiment, F1 and F2 are preferablyboth be 25 Hz. Using partial signals with very different spectralcontent than the vector signals may enable and the non-target regions tobe stimulated in very different manners, such as with inhibitorystimulation, while the target regions are stimulated with excitatorystimulation. In another embodiment the partial signals contain energyapproximately above 4 kHz and the non-target regions are “blocked” withinhibitory stimulation while the target regions are stimulated withinterference fields that produce excitatory stimulation (Tai et al,2005).

In order to decrease the risk, or amount, of tolerance and habituation,the spectral content of the vector signal can remain approximatelyconstant, but can be generated using partial signals which change overtime (thereby altering local field strengths and orientations of voxels,within the field, although the average field signal remains constant).For example, the two partial stimulation signals can simply be exchangedfor two new signals which also generate a desired beat frequency aswould occur if signals of 20 Hz and 24 Hz were exchanged for signals of24 Hz and 20 Hz, or 22 Hz and 26 Hz. Alternatively, in anotherembodiment, the two carriers can be adjusted, for example, byperiodically or continuously roving, stepping, or otherwise adjustingtwo stimulation signals so that the beat frequency is maintained withina specified frequency range, for example 0.1 Hz to 20 Hz. Roving a firststimulation frequency from 20 to 25 Hz while simultaneously roving asecond stimulation frequency from 26 to 31 Hz will maintain a beatfrequency of 6 Hz, in the anatomical area which receives the commonstimulation. This type of stimulation strategy may not be prone tocertain types of habituation or tolerance which may accompany simpleconstant 6 Hz stimulation. Further, if the stimulation protocol requiresa change in the modulation rate of the vector signal, then the firstpartial signal could rove from 20 to 25 Hz, while the second signalconcurrently roves from 26 to 27 Hz, causing the modulation rate of thebeat signal to rove from 6 to 2 Hz as stimulation progresses. In otherwords, the spectral content of the vector signal can be held constant orvaried while the spectral contents of partial signals are varied.

By way of illustration, by stimulating at two or more leads with tworelatively high frequency carrier frequencies a beat frequency may beproduced due to the interaction of the carriers in the neural tissuewhich is the target (labeled “T” in FIG. 3), while the higherfrequencies will stimulate, with a continuous amplitude, the neuraltissue which is not a target. The characteristics of the partialstimulation signals (higher frequencies of sinusoidal or pulse stimuli)can be selected as those which do not produce effects (e.g., below orabove functional band-pass of tissue), or which produce differenteffects from the vector signal so that non-target neuronal tissue (whichexists in the area labeled “NT” in FIG. 3) is differentially modulatedby stimulation. In one embodiment, electrodes 32A and 32C can serve asanode and 32D can be cathode. Electrodes 32A, 32C, and 32D can also bemultiple-lead bipolar stimulation leads. In an alternative embodiment,which is also intended to increase focal stimulation, stimulation occursusing two or more stimulation lead contacts (e.g., 32A and 32C) whichstimulate at levels that would be subthreshold if provided individually,but which combine to produce super-threshold stimulation. The leads arepositioned and oriented so that their fields combine to stimulate atarget region (due to summation to produce adequate signal power,correct spectral content, orientation, or correct waveshapecharacteristics), while imposing subthreshold stimulation levels inadjacent areas. For example, stimulating with a 3V signal at a directbrain stimulation electrode implanted in the subthalamic nucleus (STN)will activate axonal elements in the STN, but can also activatestructures as far as 4 mm from the electrode contact. Accordingly, insome embodiments, adjacent electrode contacts may be withinapproximately 2-6 mm when using strategies where the intention is forthe stimulation fields to interact. Although FIG. 3a shows electrodesonly configured along an x-y plane, it is obvious that the stimulationleads can be arranged in a 3-dimensional configuration, for improvedshaping of the stimulation field. Accordingly, subthreshold stimulationcan be used with correctly configured stimulation leads whose fields cansummate to the extent needed for clinical efficacy (i.e. the fields ofthe partial signals combine to produce super-threshold characteristics)primarily in the region where neurostimulation is desired.

FIG. 3b illustrates an embodiment of an implantable stimulation systemincluding a device 10 having 2 stimulation conduits which are electrodestimulation arrays 30 a, 30 b having 3 contacts each and locatedbilaterally along a patient's spine. The stimulation signals can begenerated between contacts of the conduits or a distal conduit can serveas anode, cathode, or ground.

FIG. 3c illustrates an embodiment of a display screen 300 which is partof an external patient programmer which displays the shape, location,orientation and spectral characteristics of two or more stimulationfields of the partial signals and the vector field. Such a field mightbe created if the top and bottom contacts of the right stimulation array30 b were cathode and the middle contact of stimulation array 30 a wasground, where the two partial signals flank a vector field which iscontained between them. The ability to show the locations, orientations,spectral and temporal content, and shapes of both the partial signalsand the vector signals is novel to prior art such as U.S. Pat. No.6,393,325, incorporated herein by reference. The fields can also beshaped in calibration methods using phantom models or dyes which areactivated by certain types of stimulation. The external patientprogrammer can contain a wide number of display screens, modelingsoftware, and keyboard controls, and may be implemented as a laptopcomputer with telemetry means, as is well known to those skilled in theart.

FIG. 4a shows several examples of partial signals. Each signal is partof a set which can be provided at 2 different leads. The sets of partialsignals will combine to form a desired signal (a vector sum of the twopartial signals) at or near the target tissue while stimulating with thepartial signals outside of the target region. In row A, a wideband noisesignal is shown in column 1, labeled “Signal #1”, which when added tothe “Signal #2” of column 2 will result to the “combined signal” shownin column 3. In row B, two pseudo-random low-pass signals are shown,which produce the combined field seen in column #3. Row C shows a chirpwaveform with energies from 10 Hz to 20 Hz, as Signal #1, and also showsa Signal #2 which can be added to it to obtain the combined signal shownin column 3. In Row D, column #1 shows a rectified amplitude modulatedcarrier (i.e., there is a DC offset) where the carrier is 30 Hz and themodulation frequency is 6 Hz and Signal #2 shows the signal which mustbe added to obtain the combined signal shown in Column 3. In rows A-D,Signal 1 and Signal 2 may each serve as partial signals in order toinduce the 6 Hz vector signal in the neural tissue commonly stimulatedby both fields. The frequency content of the partial signals shown incolumns 1 and 2 are unique from that produced in the combined signals ofcolumn 3. Accordingly, only those partial signals which produce desiredeffects can be selected to be included in the set of stimulation signalsused during treatment, while the vector signal can be maintained. In RowE, a carrier frequency at 25 Hz comprises Signal #1, which when added toa 31 Hz carrier which is Signal #2, will result in a combined signal,which is the amplitude modulated beat waveform of Column 3. It should benoted that if Signal #1 has a positive DC offset and Signal #2 has anegative DC offset, that both signals can effectively exert a bias(e.g., to polarize their respective local non-target regions), while thetarget region near a ground electrode would experience a charge balancedfield. By alternating the DC offset of the two partial signals, fromtime to time, the non-target areas would experience, over time, chargebalanced stimulation as well. The utilization of DC biasing may also beimportant for improving transmission of energy from the electrode totissue (Johnson et al, 2005).

In FIG. 4b , an additional number of examples of partial signals areshown having certain characteristics relative to the those of theheterodyne signals of column 3, and offer objects and advantages notdescribed in the prior art. In the first row of FIG. 4b , two saw-toothpulses serve as the partial signals and these combine into a vectorsignal which is a square wave at the same frequency. This type ofsummation reflects an advantage that each cycle of a pulsatile waveformcan be individually shaped to achieve desired results. In this case, thepartial signal has pulses that are significantly briefer than the pulsesof the summated signal. The time-energy characteristics of each of thepulses of the partial signals may therefore be subthreshold, while thevector field is super-threshold. In this case, partial signal 1 wassubtracted from the combined signal in order to obtain partial signal 2,as may occur in the partial signal creator 42 or related methods 52, 82,92. While only unipolar pulses are shown, bipolar pulses can also beimplemented. In the second row, two pulse trains presented at F Hz, witha time lag, are combined to produce signal with a frequency of 2 F. Bychanging the lag, different shapes of the pulse-train can be created. Inone embodiment of the method of the invention, when multiple electrodesare used, each can fire in a non-burst manner with a time lag whichproduces a “burst-train”, or paired stimulus with a specified interval,in the vector field. By tailoring the pulse patterns of the partialsignals according to the properties of the target and non-target brainregions, any pattern of bursting, non-bursting, repetitive bursting, orother patterns as are known well in the art, can be differentiallyevoked. Additionally, in a treatment where higher frequencies are usefulfor preventing certain aspects of a disorder, while lower frequenciesare useful for preventing others, then the lower frequencies can be usedas the partial signals which stimulate certain areas and also heterodyneto produce faster frequencies in the target area. In the third row tworectified sine-waves, with signal 2 inverted, are combined to produce asine function over a larger range. This embodiment can be useful, forexample, when either positive or negative stimulation at a particularelectrode leads to unwanted side-effects, while the opposite is nottrue. Lastly, in the fourth row, two amplitude modulated pulse-widthsignals are shown having different offsets, and wherein the repetitionrate (frequency of modulation) is doubled in the combined field.

Partial signals which are applied to the non-target region can beselected which are unlikely to stimulate that area in an undesiredmanner. A sufficiently fast carrier frequency may affect neural tissueonly at the onset of a train because it exceeds the chronaxie of thetissue and is thus “invisible”. Alternatively, carriers in selected highfrequency bands (e.g., 2-6 kHz region) can excite, inhibit, or ‘freeze’non-target regions, while this spectral content is not imposed in thetarget region. A pulse shape or duration, relative to its current orvoltage, or the interpulse-interval or frequency can be set so that thefield fails to entrain, or produce side-effects in, the NT area, whilethe vector field contains pulses that are entraining (e.g., FIG. 4B).Further, in paired pulse stimulation paradigms, the priming pulse can beprovided at a different set of electrode contacts than the secondarypulse so that the area exposed to both pulses is increasingly localizedto the target region. This is an advantage when the paired pulseparadigm is used to test the reactivity, or excitability, of a region,and is not described in the prior art.

The partial signals can be used with bipolar leads which are near eachother, or can be generated by monopolar leads which serve as cathode oranode and which work in conjunction with a further lead that, forexample, serves as ground. Each electrical contact may be a ground,isolated, mono-polar or bi-polar with respect to anode/cathodeassignment. When operated in a bipolar mode, one of the lead contactscan serve as a ground or opposite polarity relative to the othercontact. Alternatively, the shell of the stimulator 10 can serve asanode, cathode, ground or may be floating. Other combinations ofpolarities are possible as well, for example the shell of the stimulator10 can be divided into different sections which are electricallyisolated from each other, and when more than one stimulator 10 is used,each may have a shell that with a different electrical function, as mayoccur when the methods are implemented using stimulators such as theBION™. When multiple stimulators are used to provide the partialsignals, these may have their grounds and power-sources connected toprovide a common ground or power-source, or may be electricallyindependent.

In one embodiment, the partial signals in column 2 can be generated bysubtracting the signals in column 1, from the signals in column 3(within each of the respective rows for FIG. 4). In order to generatethe appropriate signal #2, the neurostimulator can have an analogsubtraction circuit or software routine which subtracts a given signal#1 from the desired base signal in order to generate signal #2, Thisoperation can occur in within the partial signal creator 42 of FIG. 2a ,which can utilize a specialized subtraction circuit or a softwareroutine, which is part of the stimulation subsystem 22. The partialsignal creator 42 can also have modules which take account of thegeometry of the implanted leads with respect to each other and theneurostimulator, the tissue resistance, relative polarities, and groundcontacts, with respect to the neurostimulator system, and which adjustthe characteristics (e.g., amplitude) of the partial signalsaccordingly.

Another method of creating the partial signals is shown in FIG. 5a , andcomprises the step of creating a low frequency base signal 60 which isintended as the vector signal which will be created by the summation ofthe partial signals in the stimulated tissue. The low frequency signalis added to a 1^(st) interference signal 62 a to create a first partialsignal, and then added to a 2^(nd) interference signal to create asecond partial signal 62 b, and this process is continued until all thepartial signals are created. The interference signal can have a spectralcontent which is lower or higher than the base-signal, or can haveapproximately the same content, but may act to shape the partial signalsso that these are somewhat different than the base signal (e.g., have adifferent shape). If the two partial signals do not need to havedifferent spectral characteristics, then the 2^(nd) interference signalcan simply be the 1^(st) interference signal, inverted. The interferencesignals can also simply be DC offsets and still offer advantages. If oneelectrode contact is provided with an arbitrary signal which has apositive DC offset and a second electrode contact has a differentarbitrary signal with a negative DC offset of similar magnitude, thenthe tissue near the contacts may be polarized, while the sum field willmerely have the vector field summation without DC offset. The partialsignals are then each applied to a selected contact 74. Step 74 canoccur continuously, repeatedly, responsively, or according to alternatestrategy as dictated by the treatment program. The partial signals canbe re-assigned to the same or different contacts in subsequentiterations. In step 74, the partial signals can be altered in magnitudeand polarity based upon the 3D geometry of the electrodes, impedances,etc. Circuitry or software can model the field summation, and adjust thesignals. Nodal, loop, mesh, current source density, finite elementanalysis, dipole, field distribution, impedance, and other types ofanalysis may be implemented in deriving the field model. As these typesof analyses are computationally complex and may require human judgment,the analysis can be done offline, by medical personnel, and appropriatecoefficients, mathematical transforms, and algorithms, which reflect theresults of this analysis, can be uploaded to the device 10 and appliedor implemented in step 62 during the creation of interference signals,or in steps 74, 78, or 82, or by another module or component of thestimulation subsystem.

In a simple model, the amplitude of a partial signal can be multipliedby constants related to the relative distance of each of the contactsand from sine and cosine functions evaluated upon the angles between atarget and each of the electrode contacts, where contacts on oppositesides of a target will have angles 180 degrees apart and thus valueswhich vary between 1 and −1, where the sign is ignored or included basedupon the monopolar/bipolar mode, ground location, etc. This can be donefor angles and distances along x, y, and z axes. In other words, thepartial signals can each be mathematically back-projected from theneural target to their electrode source, or a virtual source locatedbetween the active contact and ground, in order to determine thewaveforms used at the source. Additionally, as indicated by the arrowfrom step 74 to step 60, this process can be repeated if the lowfrequency base signal or the partial signals require replacement, forexample, as dictated by the treatment program.

In FIG. 5b , a method is shown where a base signal with high frequencyspectral content (e.g., a pulse train, paired-stimulus waveform, orarbitrary waveform) is created 76, and the interference signals areadded to this signal 78 a, 78 b, to create partial signals that areapplied at the contacts 74. A further method of providing the partialsignals is shown in FIG. 6. The first step is to create a basestimulation signal 80, then create 2 or more partial signals 82 a, 82 bby modifying the base signal. Partial signals can be created bydistributing the base signal spatially and/or temporally across thedifferent contacts, and then applying each partial signal to a uniquecontact 74. As the figure shows, the steps 80, 82 and 74 can be repeatedin a loop to provide adjustment of the partial signals and/or basestimulation signal. If the stimulation signal is to remain constant andonly the partial signals are to be adjusted then only steps 82 a, 82 band 74 need be accomplished. All three steps can occur approximatelysimultaneously and continuously. In other words, rather than providingthe partial signals in a circular buffer which is filled in steps 82 aand 82 b, and which is then unchanged, the buffer can be updated whereinnew data are read into the buffer as old data are transduced andprovided at the contacts 32. Further, although partial signal 1 andpartial signal 2 must be applied to specific contacts 32 in order toproduce the vector field summation of the stimulation signal, theassignment of these signals to different electrode contacts can changesomewhat easily. For example, after a specified amount of time thecontacts for the first and second partial signals are switched (e.g.,step 84 of FIG. 6). In one embodiment, after a specified duration, thesignals used at lead contact 1 become signals for lead contact 2, andvice-versa. Local fields produced near the leads will change, while thevector field evoked in the target tissue will remain approximately thesame (or may be inverted). It is obvious that when more than 2 partialsignals are needed, steps 82 a and 82 b, for example, are extended tosteps 82 c, 82 d, etc. (although not shown in FIG. 6) Depending upon thenumber of electrode contacts and their geometry, during this type ofswitching, the partial signals may be rescaled, phase shifted, orinverted in order to maintain the field summation in the target tissuewhich is intended by the treatment program. This strategy ofre-assigning partial signals to selected contacts may be useful inovercoming some types of habituation or in decreasing unwantedside-effects which may be specific to a particular spectral or temporalcomponent being emitted from a particular lead. When the stimulator 10is an external TMS device, and instead of contacts, the stimulation isbeing produced by TMS coils which induce magnetic fields in the brain,the re-assignment of partial signals may be even more important sinceunlike implanted electrodes, the fields will affect the activity ofsignificant portions of tissue outside of the target area. Re-assigningpartial signals to different electrodes may be computationally lessintensive than repeatedly creating new partial signals, which is anadvantage when implemented by an implantable device, since it utilizesless power.

In yet another alternative embodiment, the assignment of pairs ofpartial signals can be altered in order to decrease habituation and inresponse to side-effects or provide other advantages. For example, if a6 Hz stimulation field is found to be efficient in blocking seizures,but one set of partial signals is found to cause side effects, then thisset can be exchanged for a different set of partial signals that resultin the same final vector field. The patient or physician can participatein this selection, or the sets of partial signals can be determinedautomatically, as therapy progresses, based upon sensed data. Referringto FIG. 4a , if the set shown in row A produces side effects then theset shown in row B can be used since both will produce the same combinedsignal. Further, the frequency content of the partial signals can alsobe altered based upon considerations such as transmission of the signalthrough tissue, capacitance or resistance issues, efficacy to entrain ormodulate tissue, or other factors. For example, if using carriers of 400and 405 Hz provide better entrainment at 5 Hz than carriers of 200 and205, then this prior set of carriers may be preferentially selected.

In another method of using partial signals to treat a disorder, (termed“trial and error method” or TAEM) two or more stimulation conduits arearranged sufficiently close that a portion of their fields will interactdue to the size of the fields that will be created by two or morestimulation signals which will be used in treatment. A first partialstimulation signal is provided by the first conduit and is heldconstant. A second stimulation signal is then applied to a secondconduit, and this field is adjusted until therapeutic benefit isobtained. In a preferred embodiment the first and second stimulationsignals have different temporal or spectral characteristics. If thestimulation is therapeutic and there are no unwanted side effects thenthose two signals can be selected for use in therapy, while ifside-effects occur then that set of partial signals is rejected. Thisprocess can iteratively repeated for different sets of two or morestimulation conduits, where subsets of the conduits can providestimulation waveforms which are identical, similar or unique to eachother. The settings which produce successful treatment therapy with noside-effects are stored in the database 28 for later use during thestimulation therapy. Additionally, the database 28 can storecombinations which have been successful with similar electrodeconfigurations in prior patients. When therapy is successful, thevoltage or current of the stimulation settings can be increased in orderto determine the limits at which the signals can be provided without theinduction of side-effects. The database 28 can store sets of partialsignals which are successful, and which are organized according to thecurrent or voltage level which will be used so that if the patientincreases the voltage or switches the partial signals, these changeswill incorporate correct signals and amplitudes. In general the TAEMmethod can be summarized in a number of steps including: providingpartial stimulation signals at two or more stimulators in a manner thatwill cause at least partial overlap of their fields; iterativelyadjusting the stimulation parameters of at least one partial signal todetermine successful partial stimulation signals (where successfulsignals provide at least some therapeutic benefit and relatively smallside-effects); selecting those combinations of partial signals whichproved successful and discarding the partial signals which were notsuccessful; implementing successful signals in therapeutic treatment. Aswith the other methods which are described herein, the TAEM method canbe improved by ranking the successful signals according their success,and biasing the treatment to select and apply the better signalsaccording to their rank. The TAEM method can also be improved byperforming a meta-analysis of the signals that were successful, andthose which were not successful, and extrapolating, by computer programor other means, the characteristics of the vector fields that would havebeen created during stimulation. By analyzing the properties of thevector fields that would have been created for the successful signalsand rejected signals, it is possible to infer the common characteristicsof the vector fields which provided therapy. However, while possible,the TAEM methods described here are much less promising, and laborintensive, relative to the other methods of the invention because thereare almost an infinitely large assortment of possible combinations ofpartial signals.

In another method, termed the reverse-TAEM method, a partial signal isprovided and alternated until it provides therapeutic benefit. Whenproviding the partial signal causes unwanted side-effects, for instanceas may occur when the voltage is increased to maintain symptom relief,the application of one or more other signals is provided in order toattempt to decrease side effects while maintaining therapeutic benefit.The TAEM and reverse-TAEM methods, and variations thereof can beaccomplished during the initial setting of stimulation parameters, aswell as periodically, as needed, during therapy by patient or physician.It is believed that in actual practice these types of trial and errorstrategy would produce significantly less benefit than other methods ofthis invention, because the number of possible combinations of partialsignals are close to infinite, and information about the vector fieldsignal is either ignored, or used in a very inefficient fashion.

General embodiments of methods of adjusting partial signals should relyupon knowledge of the base signal and vector field. Accordingly, in thefirst step different base signals are sequentially presented from allelectrodes, and stimulation waveshapes which are best at reducingseizures can be determined, and become candidate stimulation basesignals. However, if some of these candidate base signals utilizepartial signals which produce side-effects, then sets of partial signalscan be created and tested in order to determine if these are alsoeffective at producing therapeutic effects while not producing unwantedside-effects of the base signals. Those partial signals which provideefficacious treatment, while not producing side-effects, can be selectedfor treatment. Additionally, it may be that certain sets of partialsignals only produce unwanted side-effects when these are used with aspecific range of voltage or current levels or even at particular leads.Accordingly, these partial signals may work well at lower levels or whenassigned differently to the available leads. The selection of thepartial signals can be based, in part, upon what voltage is required toproduce the desired therapeutic effects. For instance, the partialsignals of row A in FIG. 4a may work better at lower voltage levelswhile the set shown in row B works better at higher voltage levels. Thistype of relationship can be represented in the stimulation strategyimplemented by the treatment program so that as the voltage increases,the partial signals are altered or substituted. For example, as voltageincreases, the frequency content of the partial signals can also beincreased, by switching to different sets of partial signals which havea higher frequency content. This can occur in a continuous or stepwisemanner, and can occur based upon control laws. The selection andassignment of partial signals, or sets of partial signals, can thereforebe selected based upon a characteristic of the treatment protocol suchas overall voltage or current level. The different spectral and temporalcharacteristics of the partial signals can be modified according tooverall stimulation level with consideration of the time-energyrelationship of the stimulus to the average strength duration curve ofthe target cells. When partial signals are chosen in the context ofthese other considerations, this can occur according to “stimulationcontext rules”. It is contemplated that as these techniques areincreasing used, the stimulation context rules which work across apopulation, and even in relation to certain side-effects will becomeknown, and these can be incorporated into the stimulation protocol.

FIG. 8, shows a further embodiment of a method used in the creation ofpartial signals which occurs by processing the base signals according toan algorithm. In the first step the stimulation signals are created 90and these base signals are then processed 92 in order to producemodified signals which are used to stimulate at each of one or morecontacts 94. The processing can rely upon, for example, a filteringalgorithm which can filter the stimulation signals with differentband-pass filters in order to create unique, and spectrally orthogonal,partial signals which will combine to approximate the base signal.Further, even if only one electrode contract is used for thestimulation, the step of processing the base signal 92 can provide anumber of novel stimulation signals with a decreased amount ofcomputational power or at least less specialized components or softwaremodules. Instead of requiring a specialized algorithm for computing achirp waveform (which may not exist in generic stimulation devices), astandard random-noise signal generator can be filtered by severalband-pass filters over time, or by a programmable band-pass filter whosecentre frequency is changed over time. Both random noise generation anddigital filtering can be accomplished by components or algorithms commonto generic implantable devices. The processing of step 92 can beaccomplished by circuitry of the stimulation subsystem 22 and can occuraccording to stimulation protocols stored in the database 28 of thestimulator 10. Alternatively, all stimulation signals, and base orpartial signals can be predefined by the user and stored in the database28 to be accessed by control subsystem 20 in order to provide astimulation protocol to the stimulation subsystem 22. Creation of thebase signals and partial signals can both be accomplished by a functiongenerator of the stimulation subsystem 22 and the signals can beselected or adjusted based upon the stimulation protocol andresponsively.

In some applications where sensing is used in combination withstimulation, sensed data can lead to responsive stimulation or tochanges in basal stimulation. The electrical artifact created by thestimulation makes sensing of physiological signals during thestimulation difficult because the stimulus artifact may be larger thanthe electrical signals which are produced by the brain. Further, whenthe stimulation occurs at the same frequency as the biological signalwhich is to be measured, it is very difficult to disentangle the sensedsignal from the signal generated by the stimulator.

If the stimulation is chronically applied and the neurostimulator alsosenses EEG to predict/detect the onset of seizures, then the stimulationsignal should be factored into the detection algorithm (i.e., subtractedor removed from the sensed data). When the stimulation occurs using asignal having only high frequency spectral content e.g., 180 Hz pulsetrain, then the stimulation signal may not interfere with, or may beeasily removed from, the endogenous slower frequencies of the EEG whichis sensed. However, when the stimulation occurs at 3 or 8 Hz, then thiscan be intertwined with endogenously generated brain activity and canaffect the detection algorithms. When the stimulation signal is createdusing sensed activity so that its frequency content changes over time,then a digital filter may be varied to remove the stimulation signalfrom the incoming EEG. Additionally, adaptive filters, such as Kalmanfilters, or independent component analysis, can be used to remove theenergy related to the stimulation signal from the sensed data.

Two additional types of strategies can assist in enabling sensing toapproximately co-occur with stimulating as will now be described.Firstly, using a modulation signal (e.g. 20 Hz) with a carrier signalwhich has a much higher frequency content (e.g., 1000 Hz) can cause thestimulated tissue to be stimulated at 20 Hz, while the stimulus energyexists at 980, 1000, and 1020 Hz. If the filter of a sensor has alow-pass cut-off of 250 Hz, then the energy which is sensed at 20 Hz,should be primarily physiological, and will only be contaminated byrectification of the stimulation signal. Secondly, using partial signalsthat have spectral content which is in a different range than the signalwhich is to be sensed can enable certain types of sensing to occur. Forexample, using the partial signals in Row A or E of FIG. 4a , andfiltering the sensed data with a low-pass filter which is sufficientlyabove the primary frequency component of the vector field so that thismay be measured, should enable separation of stimulus artefact from abiological rhythm at the same frequency as the modulation of the vectorfield, since the heterodyne signal should not exist much outside of thetarget tissue. In one example, the stimulation electrodes and thesensing electrodes are located sufficiently distal that the vector fieldis not sensed by the sensing electrode. In that instance the sensingelectrode is implanted with some consideration of the electrode geometryof the stimulation contacts. In cases where the strategies justdescribed do not permit separation between stimulus artefact and thephysiological signal, the sensing can occur in a different modality. Forexample, optical, thermal, chemical or other sensing can occur whichwill not be compromised by simultaneous electrical stimulation.

Stimulation Strategies and Temporal Partial Signals.

Rather than distributing a base signal into partial signals whichconcurrently stimulate across a number of leads, partial signals can beprovided in a consecutive manner with partial temporal overlap or nooverlap. In one example of this method, shown in FIG. 9 a method ofproviding stimulation uses a multiple lead stimulator in which the basesignal is separated into partial signals that are distributed acrossmultiple contacts located either on different leads, or on amulti-contact lead, and the partial signals are temporally distributedacross the contacts. In the simplest form, a base signal can be dividedinto, for example, N partial signals and each of these partial signalsis used to stimulate particular contacts of N possible contacts. Again,characteristics such as polarities and magnitudes may be alteredaccording to the relative position of the contacts with respect to thetarget tissue, and/or the energy transfer characteristics of thecontacts (e.g., impedances), so that the stimulation signal in thetarget tissue approximates the base signal as if it had been deliveredfrom a particular lead. Each of the N partial signals can be deliveredat a different time, or can have some overlap in time with other partialsignals being delivered in order to additionally provide for fieldsummation. This strategy can have several advantages. Because thestimulation is generally provided by assigning the stimulation signal todifferent leads, at different moments in time, the signal which isprovided at any particular lead may repeat, or may be unique, even ifthe stimulation signal itself, integrated across time and leads, remainsconstant. Accordingly, temporally distributing the base signal intosub-signals which are assigned to different leads is one method ofdecreasing the risk of adaptation. This type of strategy may also reduceside-effects, since it can stimulate with a pulse train burst in theneural target, while the individual contacts stimulate with pulses in anon-burst manner. In an example of a preferred embodiment a 3 Hzsinusoidal frequency is distributed to each lead of a multiple leadstimulator (or contact of a multi-contact lead), which stimulates foronly a portion of the base signal. These segments of the base signal aretermed a “sub-signals”. The summation of the sub-signals across all theleads will result in the base stimulation signal with respect to targettissue, but not with respect to surrounding tissue. In FIG. 9, a signalis temporally divided into N sub-signals signals 100. In the next step102, each sub-signal is assigned to M contacts, and then these Mcontacts consecutively provide the stimulation signal to the targetneural tissue 104. Rather than consecutively activating single contacts,two or more of the M contacts can provide stimulation at the same time,and when these contacts are close enough that their fields can summate,then the sub-signals are also considered to be partial signals whichwill produce a vector field approximating a base signal.

An example which illustrates this method is now more specificallydescribed. A 3 Hz sinewave signal can be distributed into 6 sub-signalswhich are distributed across 6 leads, such that each sub-signalstimulates for half a cycle of the stimulation function. Although noneof the leads actually stimulate using the stimulation signal, the 6leads are activated with the appropriate lag such that the generatedsignal, from the perspective of the target neuronal population, is thereconstituted base signal. This approach can be utilized when using anystimulation signal, regardless of whether this is a burst stimulus,pulse-train, noise or a sinusoidal signal. Because each lead willstimulate using a sub-signal, the stimulation protocol can be adjustedso that each subsequent sub-signal emitted by a specific lead willalways be unique from the prior signal which it generated. For example,each lead may stimulate using a sub-signal which represents of a cycleof the stimulation signal, so that each subsequent stimulation from eachelectrode will occur with a new phase, In this example, the intervalbetween stimulation of consecutive contacts could be 125 msec and thefollowing leads will output the following cycles of the stimulationsignal in units of wavelength 1=0-0.75 (i.e. the first electrode outputs75% of a cycle of the stimulation frequency), 2=0.75-1.5, 3=1.5-2.25,4=2.25-3, 5=3-3.75, 6=3.75-4.5, 1=4.5-5.25, 2=5.25-6, etc. Using thistype of distributed stimulation paradigm may decrease the effects oflocal tolerance, electrical impedance/capacitance, or emergence ofside-effects due to a specific wave-shape, frequency of spectral energy,or other characteristic of the stimulation signal, being emitted from aparticular source.

Additional Spectral Considerations

Small changes in spectral characteristics of arbitrary signals as wellas pulse-trains can have significant effects in terms of providingtherapeutic benefit of neurostimulation. The electric fields generatedby the neurostimulation leads are dependent on both the shape of theelectrode and also on the electrical conductivity of the tissue. In thecentral nervous system conductivity is both inhomogeneous (dependent onlocation and the type of cells in that location) and anisotropic(dependent on direction or orientation of the cells with respect to thestimulation field). The inhomogeneity and anisotropy of the tissuearound the neurostimulation electrodes can alter the shape of theelectric field and the subsequent neural response to stimulation. Theresult of the neurostimulation is complicated further by the effectsthat the fields will have on the individual neurons. The secondderivative of the extracellular potentials along each process willinvoke both transmembrane and axial currents that will be distributedthroughout the neuron (a can be computed from the cable equation). Inturn, each neuron exposed to the applied field will be affected by bothinward and outward transmembrane currents and regions of depolarizationand hyperpolarization. These types of complex responses to stimulationhave been examined and verified in a large number of experimentalpreparations demonstrating the differences between anodic, cathodic, andbipolar stimulation with respect to activating and blocking neuralactivity using extracellular stimulation (McIntyre & Grill, 2002).

Accordingly, when generating a vector field by using at least twopartial signals from different electrodes, the induced electricalpotentials will be different than if both electrodes stimulated using asignal represented by the vector field (i.e., stimulating with twopartial signals that create a beat frequency may induce differenteffects than would occur by providing that frequency from two or moreelectrodes). These variations can effect energy transmission andentrainment and/or can specifically affect certain neurons in order tocompensate for the limited resources available when working withimplanted systems which rely upon fields that are generated fromneurostimulation electrodes of fixed locations.

Spectral considerations are even more important when stimulating usingextra-cranial electrical or magnetic stimulation. A stimulation signalwhich utilizes spectral energy with a center frequency of betweenapproximately 200 and 1000 Hz, may produce very different effects thanwhen using a center frequency of between approximately 1 and 100 kHz.Both of these frequency ranges can be used to deliver stimulationsignals which are used as base or partial signals. In a preferredembodiment, one or more band-pass noise stimuli are used which maydiffer widely in their spectral content, such that the partial signals,or the vector field is modulated between 0.5 and 20 Hz. The term “energybetween approximately 0.5 and 20 Hz” may be understood, in someembodiments, as a band of energy which may span 1 Hz or more. Forexample, the band of energy may span approximately 4 Hz and be centeredat 6 Hz, and may be asymmetrical, with slightly more energy at the 2higher frequencies of the band.

Using Scores and Context Rules to Provide Neurostimulation

In addition to the novel methods and signals just described, the currentinvention contains novel methods for providing or altering stimulationin response to sensed data. These methods can be used both withconventional stimulation techniques or with partial signals. In theprior art, if analysis of sensed data results in the detection of anevent then some type of change occurs, such as initiating or modifyingneurostimulation. As long as an event is detected, this change may oftenoccur identically, without consideration of: 1. the size, type, orlocation (e.g., where the event is detected with a larger amplitude byparticular electrodes) of the event; 2. whether the event is sensed atone or many of the sensors, and 3. the distances between the sensors,which may be relatively close or widely separated

In one embodiment of the present invention sensed data are processed toproduce scores, and stimulation can be applied according to thesescores. Additionally, partial signals, and sets of partial signals, canbe deemed to be successful, selected or rejected, and even rankedaccording to scores. The scores can reflect an attribute of the senseddata such as the absolute size or type of activity at one or moresensors, the number of sensors where the event is detected, the relativesize of the event at each sensor, the relative size of an event comparedto the EEG spectral power in selected frequency bands, coherence orcorrelation between different sensors, for example, during the time ofthe event compared to when the event is not occurring. One or morecharacteristics of an event (e.g., the amplitude of a seizure), ismeasured in the sensed data in order to produce a score. The score canbe based upon a single characteristic of the sensed data at a singlelead, or can be multivariate where the score is determined as a functionof several predefined dimensions along which neural activity is assessed(each of which may be reflected in a term in the score equation). Scorescan also be generated based upon an evaluation of sensed data which mayoccur by combining two or more sub-scores. Scores can reflect events orstates related to the disorder, and can be evaluated in relation to pastscores past scores (e.g., compared to past scores). When evaluation ofprocessed data is used to generate scores, this process can utilizecontext rules.

Context rules evaluate an event within a temporal, spatial or othercontext in which it has occurred. For example, if the detected event hasbeen detected within the prior 1-minute period, then the score can bedoubled. The context rules can be used to enable the score to bemodified based upon different aspects of the sensed data which are atleast partially independent from the detected event. For example, scorescan be based upon EEG measures sensed from one or more sensors relatedto the QEEG profile, reflecting different states of the brain, basedupon the amount of at least one chemical substance sensed at one or moresensors, or the relative amounts of substances, the time of day, or thenumber of events detected within a specified time period.

Different stimulation parameters can be selected or adjusted in relationto the scores. For example, a score from 1 to 3 may cause the amplitudeof the stimulation signal to be increased from 1 to 3 volts, whilescores of greater than, for example, 4 may indicate a qualitativelydifferent type of activity has been detected and can cause completelydifferent stimulation signals or strategies to be used. When the scoreis a multivariate measure, different types of activity can lead to asimilar score. The score can reflect both the characteristics of anevent as well as the brain-state in which it occurs. In one embodimentof the method a first stimulation signal stimulates at least one targetarea according to a predefined treatment protocol, and sensed data aresensed at one or more sensors. A processing module processes the senseddata to generate a score, and a second stimulation signal is thenprovided according to a stimulation protocol that is determined by thescore. In this method, medical or physiological events or states aren'tthemselves evaluated, but rather characteristics of the brain systemitself is evaluated and the scores modulate stimulation in a continuousor responsive manner.

In a further embodiment basal stimulation is provided and sensed data isobtained according to a sensing protocol. The sensed data is thenprocessed to generate both a normal and an abnormal score. For example,data is submitted to a first equation which produces a normal scorebased upon evaluation of one or more measurements of the data, and asecond equation which produces an abnormal score based upon a differentevaluation of which also uses one or more measurements. Stimulation isprovided only when the two scores meet some criteria relative to eachother. For example, the abnormal score must be twice the normal scorefor stimulation to occur. A partial embodiment of this method utilizes adiscriminant analysis algorithm which provides the probabilities (i.e.,scores) that the sensed data should be classified as normal or abnormal.In this case, stimulation may only occur when the abnormal score isabove a specified level, or has a specified relation to the normalscore.

In another embodiment basal stimulation is provided and sensed data isobtained according to a sensing protocol. The sensed data is thenprocessed to generate either a normal or an abnormal score. Stimulationis provided only when a meta-analysis of the score meets some criterion.For example, abnormal scores must occur a specified number of times,possibly within a specified duration, before stimulation will occur. Ina variant of this method, a score is derived which is neither normal norabnormal, but which must be above a specified threshold in order forstimulation to occur and the scores are computed upon sequentiallysensed data. In another variant, the sum of the scores over a specifiedperiod must be above a criterion in order for stimulation to occur. Inother words, the meta-analysis may combine the scores in a widevariation of manners as is dictated by the treatment program.

In another embodiment, basal stimulation is provided, and responsivestimulation can occur according to control laws. For example, one typeof basal stimulation can occur generally during treatment in order toprevent epileptic activity, and sensed data can be processed by acontrol circuit which generates a responsive stimulation signalaccording to control laws. In one embodiment, the control laws wouldcause the amplitude of a responsive signal to be adjusted based upon theamplitude of a selected characteristic brain activity, such as atemporal pattern of brain activity.

In a further alternative method, basal stimulation therapy is provided,and responsive stimulation occurs when events are detected. In thismethod, the characteristics of the treatment program are adjusted orselected partly or completely based upon a state index, which isindependent of the characteristics of the event which was detected. Forexample, the state index can reflect different states of the brain, suchas sleeping, awake, anxious, or drowsy. These states can be definedbased upon different EEG and QEEG profiles which normally exist duringthese states in the patient. While the event triggers responsivestimulation, the characteristics of the stimulation are modified byaspects of the send data that are at least partially independent fromthe detected event.

In another example of the method, basal stimulation therapy is provided,and responsive stimulation occurs due to processed data. In this method,the characteristics of the treatment program are adjusted or selectedpartly or completely based upon a processed data. Processed data canresult in a score, an index related to measuring chaos, complexity,various Hjorth parameters, equations including weighted scores fromprevious results, and other types of measures and results. In oneexample, the analyses of the processed data is altered by at least oneof the prior events which had been detected, or scores which had beengenerated.

In a further example of the method, basal stimulation therapy isprovided, and responsive stimulation occurs due to evaluation of triggerevents. In this method, a trigger event can cause responsiveneurostimulation to occur. In an alternative method, two trigger eventsmust occur for responsive neurostimulation to occur, and a furtherrestriction may be that these must occur in a specific order, or withina specified amount of time, or both. Additionally, an event #2 may onlybe evaluated if a different event, such as event #1, previouslyoccurred. For example, a certain type of activity related to a seizuremay only be evaluated, and possibly result in responsiveneurostimulation, if another event occurred relatively recently. Thistype of strategy may be defined in a function wherein the difference intime between 2 events, which are related to epilepsy, is increased inrelation to the size of that activity, so that 2 larger events may occurwith a greater lag than two smaller events in order to lead toresponsive stimulation.

In yet another example of the method, basal stimulation therapy isprovided, and responsive stimulation occurs when evaluation of senseddata indicates that continuous stimulation is not sufficient. Forexample, sensed data may indicated that a change in state has occurredwherein the new state is more likely to produce seizures, and requires adifferent type of stimulation to occur until the state returns orreverts to a different state.

Transcranial Magnetic Stimulation Applications

FIG. 10 shows a device 4 for providing transcranial magnetic stimulationand responsive transcranial magnetic stimulation (rTMS) to a patient 38.Device 4 can be similar to that as been described in US20030028072entitled low frequency magnetic neurostimulator for the treatment ofneurological disorders' (the '072 application), which proposes a devicewhich is a head-mounted structure containing means to provide TMS fromat least 2 sources. Treatment entails applying energy in a range belowapproximately 10 Hz to the patient's brain tissue. An implantableembodiment where direct electrical stimulation is used, is alsodescribed. Similar to this and other prior art, the present inventioncan be head mounted, exist as a small portable device, or may beconfigured to stimulate any part of a patient's body.

The methods and systems described herein offer advantages over this andother prior art methods of using stimulation such as low frequencystimulation provide using either implanted and external sources. Thecharacteristics of the stimulation signals can be adjusted according toendogenous rhythms in the brain in order to increase the efficacy oftreatment can be used in the rTMS treatment. Accordingly, the pulses,carrier or modulation waveforms of the treatment can be matched to, ordivergent from, spectral characteristics sensed within the patient'sbrain or body (by sensors which are implanted or external to thepatient, and which may exist within other instruments). This type oftreatment could be enabled, for example, using an EEG amplifier and anelectrode attached to the surface of the patient's head. The amplifiermay be physically disconnected from the electrode during periods ofpulsed magnetic stimulation so that currents are not induced in theelectrode wire. Optical probes, placed on the scalp, could also be used.The sensed data can be obtained prior to treatment or in the periodsbetween treatment pulses, which may occur in a regular, periodic manneror in response to evaluation of the EEG that is sensed. The use ofpartial signals, having unique spectral or temporal characteristics, canalso be utilized by configuring the geometry of two or more stimulationcoils appropriately with respect to the intended neural target. Sincefields from external coils must travel through intervening tissue inorder to arrive at their targets, the use of partial stimulation signalsis well suited to the rTMS application.

When the rTMS treatment is used for treating disorders such asdepression, the stimulation is can be primarily directed to the frontalareas of a patient's brain, and within the frontal areas the treatmentmay be primarily lateralized to either the left or right hemisphere,although both hemispheres can be treated. In one embodiment, whentreating disorders such as depression, the rTMS stimulation can bepulsed or modulated primarily above 20 Hz, although the vector field maybe modulated at a rate below this frequency. The use of partial signalsand vector fields may be applied to TMS applications including inductionor facilitation of anesthesia either with or without concurrent drugtherapy, electrochemotherapy, therapies that affect the permeability ofthe blood brain barrier, applications of TMS to stroke recovery andother types of adaptation, the modulation of cellular and metabolicprocesses, and other therapeutic methods and applications.

In one embodiment, the external stimulation can occur using one or moreof electric, electromagnetic, optical, laser, or RF field stimulationfrom outside the head. Stimulation may utilize spectral energy in theultra-high frequency (UHF) range, for example, 400 kHz to 150 mHz in itscarrier signal. Frequencies in this range may be provided to enablecertain benefits, such as better transmission of energy from thestimulator into the brain of the patient or better entrainment of thebrain by the stimulation, as long as considerations are taken to avoidtissue damage. This carrier signal can be pulsed or modulated at brainfrequencies from, for example, 0.1 Hz to 40 Hz, or higher ranges ifareas such as the cerebellum, reticular activating system, or brainstem,are to be stimulated. By adjusting the modulation of the energy so thatthis matches the internal rhythms of the brain, either in aspects oftemporal or spectral content, or phase or delay with respect toendogenously generated rhythms, the rhythms can be augmented (Bawin etal, 1973) or diminished. Treatment strategies may also selectneurostimulation signals that are at different frequencies than thosewhich occur endogenously, in order to provide certain types of treatmentor in order to avoid interfering with certain endogenous processes.

Treatment

When using the stimulation methods described herein, targets forstimulation can be any part of an organism, for example, targets may beneural, vascular, in the brain spinal cord, heart, digestive system, ormuscle or organ. Targets used in the treatment of different disorders(e.g., epilepsy, migraine, psychiatric, neurodegenerative, memory,eating, pain, sleep, mood, anxiety, movement disorders, and tremors) mayinclude, but not be limited to the one or more regions of thehippocampus, cortex, especially the frontal or motor cortex, brainstem,thalamus, and spinal cord, or at least one nerve structure comprises atleast one of the vagus nerve, a trigeminal nerve, a branch of thetrigeminal nerve, a trigeminal ganglion, an ophthalmic nerve, amaxillary nerve, a mandibular nerve, a greater occipital nerve, a lesseroccipital nerve, a third occipital nerve, a facial nerve, or aglossopharyngeal nerve.

The stimulation methods described herein can be used to stimulate tissuein order to modulate electrical, chemical, metabolic, or other types ofactivity, as well as cellular and developmental processes. The methodsand systems for generating electrical fields can be applied to therapiesand procedures related to growth and differentiation of cells (e.g.,pre/post-implantation procedures related to stem or fetal cells),including neural differentiation which is induced by electricallystimulated gene expression (Mie et al, 2003). Further, the methods andsystems can be used in conjunction with treatments such as chemotherapyin order to potentiate the response to or uptake of chemotherapeuticagents or can be used independently as an anti-cancer therapy whereelectrical treatment of malignant tumors and neoplasms is provided byapplying vector field stimulation approximately to affected tissue.Additionally the methods and systems can be used to modulate genetransfection, or alter the uptake of drugs by cells (e.g,electroporation, electropermeabilization, DNA electrotransfer) and canalso be applied to modulate cellular growth and proliferation (Miklavcicet al., 1998; Faurie et al, 2004; Pucihar et al, 2002; Ciria et al,2004; Cucullo et al., 2005). In some of these cases, great advantage maybe obtained from using partial signals when stimulating focally in the0.1 Hz to 20 Hz range, with respect to decreasing unwanted side-effectsand assisting in patient tolerance to treatment. The stimulation can beused to alter cellular functioning, particularly protein synthesis, andalter synaptic transmission by modulating the production ofneurotransmitters (Cucullo et al, 2005; Benabid & Wallace, 2005). Thetechniques can be used for wound healing, bone repair, and modulation ofcellular activity and can also be used for prophylactic treatment.Further, the methods and systems can be used in dermatological treatmentand cosmetic applications such as tissue reshaping and skin tightening,for example, by causing controlled patterns of damage, electroporation,thermal induction, wound healing, and collagen growth in selected tissueareas, such as skin, muscle, and fat. The systems and method can also beused to stimulate drugs or drug release, for example drugs stored withinnano-particles which release these drugs when triggered by specifictypes of energy. The creation and utilization of partial signalsdescribed herein can be provided by implanted electrodes, or by opticaltransducers, or by external stimulation devices such as rTMS devices.

The stimulation methods and systems of the current invention can be usedin conjunction with priming techniques. For example, subthreshold orsuper-threshold stimulation can occur prior to, stimulation with any ofthe described techniques in order to facilitate, enhance, or diminishthe response to the subsequent stimulation (e.g. Lyer et al, 2003).Likewise, post-stimulation modulation signals can be paired withstimulation signals in order to modulate, enhance, or diminish theresponse to the prior stimulation.

The contents of all prior art examples cited in this specification andall scientific and technical references, are hereby incorporated byreference as if recited in full herein. In the body or claims of thisapplication, even when methods have steps which have been assignedletters, the steps may occur sequentially in the order indicated by theletters, or certain steps may occur approximately simultaneously, or inan interleaved fashion, with other steps. The headers for varioussections of this application, such as “Background” or “Treatment”, areintended to be descriptive only, and do not limit the scope of thematerial which is provided in these sections, in any way.

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It should be understood that various aspects disclosed herein may becombined in different combinations than the combinations specificallypresented in the description and accompanying drawings. It should alsobe understood that, depending on the example, certain acts or events ofany of the processes or methods described herein may be performed in adifferent sequence, may be added, merged, or left out altogether (e.g.,all described acts or events may not be necessary to carry out thetechniques). In addition, while certain aspects of this disclosure aredescribed as being performed by a single module or unit for purposes ofclarity, it should be understood that the techniques of this disclosuremay be performed by a combination of units or modules associated with,for example, a medical device.

In one or more examples, the described techniques may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored as one or more instructions orcode on a computer-readable medium and executed by a hardware-basedprocessing unit. Computer-readable media may include non-transitorycomputer-readable media, which corresponds to a tangible medium such asdata storage media (e.g., RAM, ROM, EEPROM, flash memory, or any othermedium that can be used to store desired program code in the form ofinstructions or data structures and that can be accessed by a computer).

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablelogic arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor” as used herein may refer toany of the foregoing structure or any other physical structure suitablefor implementation of the described techniques. Also, the techniquescould be fully implemented in one or more circuits or logic elements.

What is claimed is:
 1. A patient treatment system comprising: animplantable pulse generator programmed to provide a first pulsedelectrical signal having at least one frequency selected within therange of from about 1 kHz to about 100 kHz; and at least a firstimplantable electrical lead with a first set of electrical contacts fordelivering the first pulsed electrical signal to at least one locationalong a patient's spinal cord to treat pain in the patient throughapplication of the first pulsed electrical signal; and wherein thepatient system is configured to provide the first pulsed electricalsignal without the first pulsed electrical signal producing an unwantedside-effect related to sensory processing.
 2. The system of claim 1wherein the first pulsed electrical signal is realized as a modulatedcarrier signal.
 3. The system of claim 1 wherein the first pulsedelectrical signal is realized as a modulated carrier signal with amodulation signal selected to avoid producing said unwanted side-effectrelated to interference of sensory processing.
 4. The system of claim 1wherein the patient treatment system includes a second implantableelectrical lead with a second set of electrical contacts.
 5. The systemof claim 4 wherein the implantable electrical leads are configured forplacement bilaterally along a patient's spine.
 6. The system of claim 1wherein the first pulsed electrical signal is configured to provideinhibitory stimulation to nerves.
 7. The system of claim 1 wherein theat least one lead includes at least one electrode configured to operateas stimulating electrode and a sensor.
 8. The system of claim 7 furthercomprising a sensor subsystem configured to measure impedance sensed atthe least one electrode.
 9. The system of claim 1 wherein the firstpulsed electrical signal is further realized as a modulated carriersignal selected to avoid producing an unwanted side-effect related tointerference of at least one motor process.
 10. The system of claim 1wherein the implantable pulse generator is programmed to provide thefirst pulsed electrical signal at the selected frequency being furtherselected to deter a side-effect related to interference of a motorprocess.
 11. The system of claim 1 wherein the implantable pulsegenerator is programmed with a stimulation protocol that creates thefirst pulsed electrical signal with biphasic pulses.
 12. The system ofclaim 1 wherein the implantable pulse generator is programmed to providethe first pulsed electrical signal at a frequency of from about 2 kHz toabout 6 kHz.
 13. The system of claim 1 wherein electrical contacts of astimulator used to provide the pulsed electrical signal are spaced apartfrom each other by a distance and geometry that is selected or adjustedin relation to an intended superposition of signal components of avector stimulus waveform.
 14. The system of claim 1 wherein theimplantable pulse generator is programmed to provide the first pulsedelectrical signal at the selected frequency within the range of about 4kHz to about 100 kHz.
 15. The system of claim 1 wherein the implantablepulse generator is programmed to provide the first pulsed electricalsignal at the selected frequency, wherein the frequency is selected toincrease transmission of the signal through tissue compared to a lowerfrequency range than the frequency range between 1 kHz and 100 kHz. 16.The system of claim 1 wherein the implantable pulse generator isprogrammed to modulate the first pulsed electrical signal using aselected modulation frequency within the range of approximately 0.1 Hzto 40 Hz.
 17. The system of claim 1 wherein the unwanted side effectincludes paresthesia.
 18. The system of claim 1, further including asensing subsystem having at least one sensor positioned to detect asensed data including an evoked response to the first pulsed electricalsignal, the system configured to adjust a characteristic of the firstpulsed electrical signal based upon evaluation of a characteristic ofsensed data.
 19. The system of claim 1, further including a sensingsubsystem having at least one sensor configured to sense sensed datarelated to the patient, and an evaluation subsystem configured toevaluate the sensed data and adjust at least one stimulation protocolparameter of the first pulsed electrical signal upon evaluation of thesensed data.